This invention relates to flash-memory-card readers, and more particularly to data exchangers.
Consumer devices such as digital cameras and personal digital assistants (PDAs) often use removable flash memory. The removable flash memory is in the form of a small card in a standardized form factor such as compact flash (CF), secure digital (SD), multimedia card (MMC), or Sony's Memory Stick.
Flash memory has gained wide acceptance for its nonvolatile storage, which is ideal for portable devices that may lose power, since the data is not lost when stored in the flash memory. Flash memories are constructed from electrically-erasable programmable read-only memory (EEPROM) cells.
Rather than using a randomly-addressable scheme such as is common with dynamic-random-access memory (DRAM), many flash memories use a block-based addressing where a command and an address are sent over the data bus and then a block of data is read or written. Since the data bus is also use to send commands and addresses, fewer pins are needed on the flash-memory chip, reducing cost. Thus flash memory is often used as a mass-storage device rather than a randomly-addressable device.
Universal-Serial-Bus (USB) has become a popular standard interface for connecting peripherals to a host such as a personal computer (PC). USB-based flash-memory storage devices or “drives” have been developed to transport data from one host to another, replacing floppy disks. While large external flash drives may be used, smaller USB flash drives known as key-chain or key drives have been a rapidly growing market.
Flash-card readers are sometimes used to transfer digital data, such as digital picture files, from the removable flash card to a PC. The flash-memory card can be removed from the digital camera and inserted into a slot on the flash-card reader. The user can then copy the digital-picture files to the PC using the flash-card reader.
FIG. 1 shows a prior-art flash-card reader. Card reader 35 is a peripheral device that can be attached to host PC 10 using a serial bus such as a USB. For example, card reader 35 may be contained in a small box and attached to host PC 10 by a USB cable that plugs into USB connector 12 on card reader 35 and into another USB plug on host PC 10. Card reader 35 could also be located inside host PC 10 or inside another device, such as inside a printer. Optional battery or power adapter 14 can be used to supply power.
Serial packets from host PC 10 are transferred through USB connector 12 to USB peripheral controller 15 in card reader 35. USB peripheral controller 15 decodes commands and addresses in the USB packets and performs requested operations. For example, host PC 10 can send USB packets requesting to read data on compact-flash card 22 that is inserted into a slot in card reader 35. USB peripheral controller 15 activates compact-flash interface 20 to read data from compact-flash card 22.
Several slots for several different kinds of flash cards may be present on card reader 35, although some card readers have only one type of slot. For example, a different size slot can accept smart-media flash-card 26, while another slot accepts secure-digital/multi-media card 32, and another accepts memory stick 36.
USB peripheral controller 15 can receive interrupts from one of flash interfaces 20, 24, 28, 24 when one of compact-flash card 22, smart-media flash-card 26, secure-digital/multi-media card 32, or memory stick 36, respectively, is inserted into a slot and pushed into an electrical connector in the slot. USB peripheral controller 15 can read configuration information from the newly-inserted flash card and then send a USB packet to host PC 10. Alternately, host PC 10 can periodically search for inserted flash cards by attempting to read from each of compact-flash card 22, smart-media flash-card 26, secure-digital/multi-media card 32, and memory stick 36. When the flash cards are not inserted, the reading fails.
Card reader 35 acts as a USB peripheral, while host PC 10 acts as the USB host. The USB host sends request packets to the USB peripheral, and the USB peripheral responds to these requests, such as by reading data. Special mass-storage class software running on host PC 10 schedules USB transactions to one or more USB peripherals. Many USB peripherals can be accessed when USB hubs are used, either on host PC 10 or externally.
While card reader 35 is useful, it requires host PC 10 for operation, since USB peripheral controller 15 can only respond to USB commands from host PC 10. USB peripheral controller 15 acts as a USB endpoint, merely responding to commands from the upstream USB host on the PC. When host PC 10 is not connected, card reader 35 is not able to read flash-memory cards. card reader 35 lacks USB host intelligence since it is a USB peripheral.
Sometimes a user is not near host PC 10 and yet desired to transfer digital files from a flash-memory card to a storage media. For example, a tourist may take many digital photos and fill his flash-memory card. The tourist could take along additional flash-memory cards, or find an Internet cafe and download the digital pictures from the flash card to a recordable optical disk or to the Internet, but the Internet cafe may not have a flash-card reader.
Portable flash-card readers have been developed to solve this problem. These portable flash-card readers may contain a small hard disk, allowing the user to transfer digital picture files from a removable flash-memory card to the hard disk. Later the portable flash-card reader may be connected to a PC and the digital picture files transferred from the small hard disk to the PC. Unfortunately, the small hard drive on the portable flash-card reader may fail after experiencing shock and have reliability problems.
The portable flash-card reader may be equipped with an internal, built-in flash memory rather than the small hard drive to alleviate reliability problems. However, the portable flash-card reader may become outdated as digital-photo sizes increase, since the amount of internal flash memory is fixed. It would be better to have an expandable amount of flash memory.
What is desired is a portable flash-card reader that has an expandable amount of flash memory. A flash-card exchanger that can transfer digital files from a removable flash-memory card to an expandable and removable flash memory is desired. A flash-card exchanger that can perform the transfer to the expandable flash memory without a host PC is desirable. A flash card reader that can operate as a USB peripheral when connected to a PC, but can also act as a USB host when not connected to a PC is desired.